Critical severity · published Aug 20, 2026
CVE-2026-73253
Mongoose: TLS Hostname Verification Bypass via Overly Permissive Wildcard Matching
9.1
CVSS
0.3%
EPSS
No
On KEV
Description
Mongoose is an embedded web server and network library. Prior to version 7.22, an on-path network attacker with a wildcard certificate for a parent domain can impersonate deeper subdomains to a client using the built-in TLS stack. The mg_tls_verify_cert_san() and mg_tls_verify_cert_cn() functions in src/tls_builtin.c call mg_match(), whose wildcard can cross DNS label boundaries, so a pattern such as *.example.com can match foo.bar.example.com. The resulting hostname verification bypass permits interception and modification of TLS traffic. This issue is fixed in version 7.22.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 28% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MO
mongoose · cesanta
< 7.22 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-73253
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-73253
Patch
https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71
Issue Tracking
https://github.com/cesanta/mongoose/pull/3611
Release Notes
https://github.com/cesanta/mongoose/releases/tag/7.22
Exploit
https://github.com/cesanta/mongoose/security/advisories/GHSA-jp6g-796f-39vp
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